hey everybody it's mr smeeds and today we'll be wrapping up unit 1 with topic 1.11 which is food webs and food chains so we'll be talking about how food webs are just groups of food chains and then we'll also be talking about how changes to one organism within a food web can have effects on the other organisms in the food web so our objective for today is to be able to describe food chains and food webs and also to be able to identify the members of food chains and food webs by their trophic levels the skill that we'll practice at the end of today's video is describing a characteristic of an environmental concept using a visual model so we use food webs to just show how the flow of matter and energy happens in an ecosystem specifically from organism to organism so when one organism eats or preys on another and remember that even an herbivore eating a plant is considered predation because it's just one organism using another for its energy source that the matter and energy are going to flow from prey to predator so again even when an herbivore is eating a plant we consider that predation and these arrows are just going to show the direction of energy and matter movement so sometimes students get confused by trying to memorize that the arrows either point at the eater or the plant or organism being eaten but it's a lot easier to just remember that the arrow shows the direction of energy so the organism that the arrow is pointing at is taking in the energy and taking in the matter so for example we could look at a grasshopper here and the grasshopper is going to eat the corn and the grasshopper is going to take in the energy or the glucose from the corn it can use that for movement or for growth it's also going to take in the nitrogen and the phosphorus and the corn so it's going to use that to build more of its body and so that grasshopper is taking in the energy and the matter and that's the direction of the flow from corn to grasshopper now we'll talk about the difference between food webs and food chains so as the diagram shows a food chain is just one simple pathway of energy and matter flowing from organism to organism a food web is at least two connected food chains that share a common link so let's look at the diagram for example first we have a grass to rabbit to fox food chain and that's a chain because just one linear pathway of energy flow however if we add in a second pathway which be the grass to the grasshopper to the mouse and then to the fox again that would be a second chain and we now have a food web because these two separate chains are linked by the fox as the common organism so really important to know that food webs do not have to be incredibly complex the basic definition is just that they are at least two food chains that are connected to one another by one common organism this is really helpful for helping us visualize how organisms can occupy two different trophic levels so we have the example here of the owl the owl will be considered a secondary consumer if it's consuming the rabbit because the rabbit is a primary consumer which ate the grass but the owl is considered a tertiary consumer if it's eating a robin and that's because the robin a secondary consumer ate a grasshopper a primary consumer which ate the grass a producer so again this is a helpful reminder for visualizing how organisms can occupy different trophic levels within the food web food webs are also very helpful for understanding the interactions between organisms and ecosystem so they can help us visualize how an increase or a decrease in the population size for a given species can impact the other organisms that are part of that food web so let's look at an example here we have the python and if the python is going to increase so its population size grows that's going to lead to a decline in its prey which is the rat and the frog they're going to be fewer rats and frogs because there are more pythons eating them this is going to lead to an increase in the grasshopper population because their main predators the rat and the frog have both suffered a decline in their populations with an increase in the grasshopper population we're going to have a decrease in the corn population because there's so many more grasshoppers eating the corn so this could have a lot of other effects on the ecosystem that we haven't depicted here other organisms that rely on corn may suffer now with less corn due to the grasshoppers eating it we could also have an impact on the ego population because two of their main food sources the rat and the frog have declined so we can see that increasing or decreasing one organism's population size has a dramatic impact on the trophic levels above and below we call this a trophic cascade so trophic cascade is this idea that when we have a dramatic increase or decrease in a top predator there's kind of a ripple effect down through the tropic levels below that top predator another really common example of a trophic cascade is when we have the loss of a top predator so in this simple example we have the loss of the wolf that leads to a dramatic increase in the deer population which leads to a dramatic decrease in the plants that deer eat and so that can result in a forest that has a lot less ground cover trees that have a lot fewer leaves potentially those trees may die off and we could have a huge impact to the ecosystem because of all those other organisms that relied on the grass for habitat or food as well as the trees and so the loss of a top predator can have a really dramatic impact and one of the common impacts that it has is what we would call defoliation or the loss of vegetation in an area again because of this huge increase in herbivores like deer that without the wolf really don't have a predator to keep them in track it's important that we understand how trophic levels impact the levels below them when those population sizes either increase or decrease so for practice for q 1.11 today we're going to be practicing the skill of describing characteristics of environmental concept specifically here using a visual model so we have two frqs one is to describe a direct effect that a decline in the frog population would have on a different organism in the food web and then the second one is to identify an organism that is both a secondary and a tertiary consumer in this food web alright everybody thanks for tuning in today don't forget to like this video if it was helpful subscribe for future apes video updates and check out other notes over here to the side and as always think like a mountain write like a scholar